Synthesis of high vinyl rubber

ABSTRACT

Metal salts of saturated aliphatic alcohols can be used as modifiers in lithium initiated solution polymerizations of diene monomers into rubbery polymers. Sodium t-amylate is a preferred modifiers because of its exceptional solubility in non-polar aliphatic hydrocarbon solvents that are employed as the medium for such solution polymerizations. However, using sodium t-amylate as the polymerization modifier in commercial operations where recycle is required can lead to certain problems. These problems arise due to the fact that sodium t-amylate reacts with water to form t-amyl alcohol during steam stripping in the polymer finishing step. Since t-amyl alcohol forms an azeotrope with hexane, it co-distills with hexane and thus contaminates the feed stream. The present invention solves the problem of recycle stream contamination. This invention is based upon the discovery of highly effective modifiers that do not co-distill with hexane or-form-compounds during steam stripping which co-distill with hexane. The modifiers of this invention are metal salts of cyclic alcohols. Since the boiling points of these metal salts of cyclic alcohols are very high, they do not co-distill with hexane and contaminate recycle streams. Additionally, metal salts of cyclic alcohols are considered to be environmentally safe. The, subject invention more specifically discloses an initiator system which is comprised of (a) a lithium initiator, (b) a metal salt of a cyclic alcohol, and (c) a polar modifier.

BACKGROUND OF THE INVENTION

It is highly desirable for tires to exhibit good tractioncharacteristics on both dry and wet surfaces. However, it hastraditionally been very difficult to improve the tractioncharacteristics of a tire without compromising its rolling resistanceand tread wear. Low rolling resistance is important because good fueleconomy is virtually always an important consideration. Good tread wearis also an important consideration because it is generally the mostimportant factor which determines the life of the tire.

The traction, tread wear, and rolling resistance of a tire is dependentto a large extent on the dynamic viscoelastic properties of theelastomers utilized in making the tire tread. In order to reduce therolling resistance of a tire, rubbers having a high rebound havetraditionally been utilized in making the tire's tread. On the otherhand, in order to increase the wet skid resistance of a tire, rubberswhich undergo a large energy loss have generally been utilized in thetire's tread. In order to balance these two viscoelasticallyinconsistent properties, mixtures of various types of synthetic andnatural rubber are normally utilized in tire treads. For instancevarious mixtures of styrene-butadiene rubber and polybutadiene rubberare commonly used as a rubber material for automobile tire treads.However, such blends are not totally satisfactory for all purposes.

The inclusion of styrene-butadiene rubber (SBR) in tire treadformulations can significantly improve the traction characteristics oftires made therewith. However, styrene is a relatively expensive monomerand the inclusion of SBR is tire tread formulations leads to increasedcosts.

Carbon black is generally included in rubber compositions which areemployed in making tires and most other rubber articles. It is desirableto attain the best possible dispersion of the carbon black throughoutthe rubber to attain optimized properties. It is also highly desirableto improve the interaction between the carbon black and the rubber. Byimproving the affinity of the rubber compound to the carbon black,physical properties can be improved. Silica can also be included in tiretread formulations to improve rolling resistance.

U.S. Pat. No. 4,843,120 discloses that tires having improved performancecharacteristics can be prepared by utilizing rubbery polymers havingmultiple glass transition temperatures as the tread rubber. Theserubbery polymers having multiple glass transition temperatures exhibit afirst glass transition temperature which is within the range of about-110° C. to -20° C. and exhibit a second glass transition temperaturewhich is within the range of about -50° C. to 0° C. According to U.S.Pat. No. 4,843,120, these polymers are made by polymerizing at least oneconjugated diolefin monomer in a first reaction zone at a temperatureand under conditions sufficient to produce a first polymeric segmenthaving a glass transition temperature which is between -110° C. and -20°C. and subsequently continuing said polymerization in a second reactionzone at a temperature and under conditions sufficient to produce asecond polymeric segment having a glass transition temperature which isbetween -20° C. and 20° C. Such polymerizations are normally catalyzedwith an organolithium catalyst and are normally carried out in an inertorganic solvent.

U.S. Pat. No. 5,137,998 discloses a process for preparing a rubberyterpolymer of styrene, isoprene, and butadiene having multiple glasstransition temperatures and having an excellent combination ofproperties for use in making tire treads which comprises:terpolymerizing styrene, isoprene and 1,3-butadiene in an organicsolvent at a temperature of no more than about 40° C. in the presence of(a) at least one member selected from the group consisting oftripiperidino phosphine oxide and alkali metal alkoxides and (b) anorganolithium compound.

U.S. Pat. No. 5,047,483 discloses a pneumatic tire having an outercircumferential tread where said tread is a sulfur cured rubbercomposition comprised of, based on 100 parts by weight rubber (phr), (A)about 10 to about 90 parts by weight of a styrene, isoprene, butadieneterpolymer rubber (SIBR), and (B) about 70 to about 30 weight percent ofat least one of cis 1,4-polyisoprene rubber and cis 1,4-polybutadienerubber wherein said SIBR rubber is comprised of (1) about 10 to about 35weight percent bound styrene, (2) about 30 to about 50 weight percentbound isoprene and (3) about 30 to about 40 weight percent boundbutadiene and is characterized by having a single glass transitiontemperature (Tg) which is in the range of about -10° C. to about -40° C.and, further the said bound butadiene structure contains about 30 toabout 40 percent 1,2-vinyl units, the said bound isoprene structurecontains about 10 to about 30 percent 3,4-units, and the sum of thepercent 1,2-vinyl units of the bound butadiene and the percent 3,4-unitsof the bound isoprene is in the range of about 40 to about 70 percent.

U.S. Pat. No. 5,272,220 discloses a styrene-isoprene-butadiene rubberwhich is particularly valuable for use in making truck tire treads whichexhibit improved rolling resistance and tread wear characteristics ,said rubber being comprised of repeat units which are derived from about5 weight percent to about 20 weight percent styrene, from about 7 weightpercent to about 35 weight percent isoprene, and from about 55 weightpercent to about 88 weight percent 1,3-butadiene, wherein the repeatunits derived from styrene, isoprene and 1,3-butadiene are inessentially random order, wherein from about 25% to about 40% of therepeat units derived from the 1,3-butadiene are of thecis-microstructure, wherein from about 40% to about 60% of the repeatunits derived from the 1,3-butadiene are of the trans-microstructure,wherein from about 5% to about 25% of the repeat units derived from the1,3-butadiene are of the vinyl-microstructure, wherein from about 75% toabout 90% of the repeat units derived from the isoprene are of the1,4-microstructure, wherein from about 10% to about 25% of the repeatunits derived from the isoprene are of the 3,4-microstructure, whereinthe rubber has a glass transition temperature which is within the rangeof about -90° C. to about -70° C., wherein the rubber has a numberaverage molecular weight which is within the range of about 150,000 toabout 400,000, wherein the rubber has a weight average molecular weightof about 300,000 to about 800,000, and wherein the rubber has aninhomogeneity which is within the range of about 0.5 to about 1.5.

U.S. Pat. No. 5,239,009 reveals a process for preparing a rubberypolymer which comprises: (a) polymerizing a conjugated diene monomerwith a lithium initiator in the substantial absence of polar modifiersat a temperature which is within the range of about 5° C. to about 100°C. to produce a living polydiene segment having a number averagemolecular weight which is within the range of about 25,000 to about350,000; and (b) utilizing the living polydiene segment to initiate theterpolymerization of 1,3-butadiene, isoprene, and styrene, wherein theterpolymerization is conducted in the presence of at least one polarmodifier at a temperature which is within the range of about 5° C. toabout 70° C. to produce a final segment which is comprised of repeatunits which are derived from 1,3-butadiene, isoprene, and styrene,wherein the final segment has a number average molecular weight which iswithin the range of about 25,000 to about 350,000. The rubbery polymermade by this process is reported to be useful for improving the wet skidresistance and traction characteristics of tires without sacrificingtread wear or rolling resistance.

U.S. Pat. No. 5,061,765 discloses isoprene-butadiene copolymers havinghigh vinyl contents which can reportedly be employed in building tireswhich have improved traction, rolling resistance, and abrasionresistance. These high vinyl isoprene-butadiene rubbers are synthesizedby copolymerizing 1,3-butadiene monomer and isoprene monomer in anorganic solvent at a temperature which is within the range of about -10°C. to about 100° C. in the presence of a catalyst system which iscomprised of (a) an organoiron compound, (b) an organoaluminum compound,(c) a chelating aromatic amine, and (d) a protonic compound; wherein themolar ratio of the chelating amine to the organoiron compound is withinthe range of about 0.1:1 to about 1:1, wherein the molar ratio of theorganoaluminum compound to the organoiron compound is within the rangeof about 5:1 to about 200:1, and herein the molar ratio of the protoniccompound to the organoaluminum compound is within the range of about0.001:1 to about 0.2:1.

U.S. Pat. No. 5,405,927 discloses an isoprene-butadiene rubber which isparticularly valuable for use in making truck tire treads, said rubberbeing comprised of repeat units which are derived from about 20 weightpercent to about 50 weight percent isoprene and from about 50 weightpercent to about 80 weight percent 1,3-butadiene, wherein the repeatunits derived from isoprene and 1,3-butadiene are in essentially randomorder, wherein from about 3% to about 10% of the repeat units in saidrubber are 1,2-polybutadiene units, wherein from about 50% to about 70%of the repeat units in said rubber are 1,4-polybutadiene units, whereinfrom about 1% to about 4% of the repeat units in said rubber are3,4-polyisoprene units, wherein from about 25% to about 40% of therepeat units in the polymer are 1,4-polyisoprene units, wherein therubber has a glass transition temperature which is within the range ofabout -90° C. to about -75° C., and wherein the rubber has a Mooneyviscosity which is within the range of about 55 to about 140.

U.S. Pat. No. 5,654,384 discloses a process for preparing high vinylpolybutadiene rubber which comprises polymerizing 1,3-butadiene monomerwith a lithium initiator at a temperature which is within the range ofabout 5° C. to about 100° C. in the presence of a sodium alkoxide and apolar modifier, wherein the molar ratio of the sodium alkoxide to thepolar modifier is within the range of about 0.1:1 to about 10:1; andwherein the molar ratio of the sodium alkoxide to the lithium initiatoris within the range of about 0.05:1 to about 10:1. By utilizing acombination of sodium alkoxide and a conventional polar modifier, suchas an amine or an ether, the rate of polymerization initiated withorganolithium compounds can be greatly increased with the glasstransition temperature of the polymer produced also being substantiallyincreased. The rubbers synthesized using such catalyst systems alsoexhibit excellent traction properties when compounded into tire treadformulations. This is attributable to the unique macrostructure (randombranching) of the rubbers made with such catalyst systems.

U.S. Pat. No. 5,620,939, U.S. Pat. No. 5,627,237, and U.S. Pat. No.5,677,402 also disclose the use of sodium salts of saturated aliphaticalcohols as modifiers for lithium initiated solution polymerizations.Sodium t-amylate is a preferred sodium alkoxide by virtue of itsexceptional solubility in non-polar aliphatic hydrocarbon solvents, suchas hexane, which are employed as the medium for such solutionpolymerizations. However, using sodium t-amylate as the polymerizationmodifier in commercial operations where recycle is required can lead tocertain problems. These problems arise due to the fact that sodiumt-amylate reacts with water to form t-amyl alcohol during steamstripping in the polymer finishing step. Since t-amyl alcohol forms anazeotrope with hexane, it co-distills with hexane and thus contaminatesthe feed stream.

SUMMARY OF THE INVENTION

The present invention solves the problem of recycle streamcontamination. This invention is based upon the discovery of highlyeffective modifiers that do not co-distill with hexane or form compoundsduring steam stripping which co-distill with hexane. The modifiers ofthis invention are metal salts of cyclic alcohols. These modifiers thatprovide similar modification efficiencies to sodium t-amylate. Since theboiling points of these metal salts of cyclic alcohols are very high,they do not co-distill with hexane and contaminate recycle streams.Additionally, metal salts of cyclic alcohols are considered to beenvironmentally safe. In fact, sodium mentholate is used as a foodadditive.

The subject invention further discloses a process for preparing arubbery polymer having a high vinyl content which comprises:polymerizing at least one diene monomer with a lithium initiator at atemperature which is within the range of about 5° C. to about 100° C. inthe presence of a metal salt of a cyclic alcohol and a polar modifier,wherein the molar ratio of the metal salt of the cyclic alcohol to thepolar modifier is within the range of about 0.1:1 to about 10:1; andwherein the molar ratio of the metal salt of the cyclic alcohol to thelithium initiator is within the range of about 0.05:1 to about 10:1.

The subject invention further discloses a process for preparing highvinyl polybutadiene rubber which comprises: polymerizing 1,3-butadienemonomer with a lithium initiator at a temperature which is within therange of about 5° C. to about 100° C. in the presence of a metal salt ofa cyclic alcohol and a polar modifier, wherein the molar ratio of themetal salt of the cyclic alcohol to the polar modifier is within therange of about 0.1:1 to about 10:1; and wherein the molar ratio of themetal salt of the cyclic alcohol to the lithium initiator is within therange of about 0.05:1 to about 10:1.

The subject invention also reveals an initiator system which iscomprised of (a) a lithium initiator, (b) a metal salt of a cyclicalcohol, and (c) a polar modifier; wherein the molar ratio of the metalsalt of the cyclic alcohol to the polar modifier is within the range ofabout 0.1:1 to about 10:1; and wherein the molar ratio of the metal saltof the cyclic alcohol to the lithium initiator is within the range ofabout 0.01:1 to about 20:1.

DETAILED DESCRIPTION OF THE INVENTION

The polymerizations of this invention are normally carried out assolution polymerizations in an inert organic medium utilizing a lithiumcatalyst. However, metal salts of cyclic alcohols can also be employedin accordance with this invention as modifiers for bulk polymerizationsor vapor phase polymerizations. The vinyl content of the rubbery polymermade is controlled by the amount of modifier present during thepolymerization.

The rubbery polymers synthesized using the modifiers of this inventioncan be made by the homopolymerization of a conjugated diolefin monomeror by the copolymerization of a conjugated diolefin monomer with a vinylaromatic monomer. It is, of course, also possible to make rubberypolymers by polymerizing a mixture of conjugated diolefin monomers withone or more ethylenically unsaturated monomers, such as vinyl aromaticmonomers. The conjugated diolefin monomers which can be utilized in thesynthesis of rubbery polymers in accordance with this inventiongenerally contain from 4 to 12 carbon atoms. Those containing from 4 to8 carbon atoms are generally preferred for commercial purposes. Forsimilar reasons, 1,3-butadiene and isoprene are the most commonlyutilized conjugated diolefin monomers. Some additional conjugateddiolefin monomers that can be utilized include2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene,2-phenyl-1,3-butadiene, and the like, alone or in admixture.

Some representative examples of ethylenically unsaturated monomers thatcan potentially be copolymerized into rubbery polymers using themodifiers of this invention include alkyl acrylates, such as methylacrylate, ethyl acrylate, butyl acrylate, methyl methacrylate and thelike; vinylidene monomers having one or more terminal CH2═CH-- groups;vinyl aromatics such as styrene, α-methylstyrene, bromostyrene,chlorostyrene, fluorostyrene and the like; α-olefins such as ethylene,propylene, 1-butene and the like; vinyl halides, such as vinylbromide,chloroethane (vinylchloride), vinylfluoride, vinyliodide,1,2-dibromoethene, 1,1-dichloroethene (vinylidene chloride),1,2-dichloroethene and the like; vinyl esters, such as vinyl acetate;α,β-olefinically unsaturated nitriles, such as acrylonitrile andmethacrylonitrile; α,β-olefinically unsaturated amides, such asacrylamide, N-methyl acrylamide, N,N-dimethylacrylamide, methacrylamideand the like.

Rubbery polymers which are copolymers of one or more diene monomers withone or more other ethylenically unsaturated monomers will normallycontain from about 50 weight percent to about 99 weight percentconjugated diolefin monomers and from about 1 weight percent to about 50weight percent of the other ethylenically unsaturated monomers inaddition to the conjugated diolefin monomers. For example, copolymers ofconjugated diolefin monomers with vinylaromatic monomers, such asstyrene-butadiene rubbers which contain from 50 to 95 weight percentconjugated diolefin monomers and from 5 to 50 weight percentvinylaromatic monomers, are useful in many applications.

Vinyl aromatic monomers are probably the most important group ofethylenically unsaturated monomers which are commonly incorporated intopolydienes. Such vinyl aromatic monomers are, of course, selected so asto be copolymerizable with the conjugated diolefin monomers beingutilized. Generally, any vinyl aromatic monomer which is known topolymerize with organolithium initiators can be used. Such vinylaromatic monomers typically contain from 8 to 20 carbon atoms. Usually,the vinyl aromatic monomer will contain from 8 to 14 carbon atoms. Themost widely used vinyl aromatic monomer is styrene. Some examples ofvinyl aromatic monomers that can be utilized include styrene,1-vinylnaphthalene, 2-vinylnaphthalene, α-methylstyrene,4-phenylstyrene, 3-methylstyrene and the like.

Some representative examples of rubbery polymers which can beasymmetrically tin-coupled in accordance with this invention includepolybutadiene, polyisoprene, styrene-butadiene rubber (SBR),α-methylstyrene-butadiene rubber, α-methylstyrene-isoprene rubber,styrene-isoprene-butadiene rubber (SIBR), styrene-isoprene rubber (SIR),isoprene-butadiene rubber (IBR), α-methylstyrene-isoprene-butadienerubber and α-methylstyrene-styrene-isoprene-butadiene rubber.

In solution polymerizations the inert organic medium which is utilizedas the solvent will typically be a hydrocarbon which is liquid atambient temperatures which can be one or more aromatic, paraffinic orcycloparaffinic compounds. These solvents will normally contain from 4to 10 carbon atoms per molecule and will be liquids under the conditionsof the polymerization. It is, of course, important for the solventselected to be inert. The term "inert" as used herein means that thesolvent does not interfere with the polymerization reaction or reactwith the polymers made thereby. Some representative examples of suitableorganic solvents include pentane, isooctane, cyclohexane, normal hexane,benzene, toluene, xylene, ethylbenzene and the like, alone or inadmixture. Saturated aliphatic solvents, such as cyclohexane and normalhexane, are most preferred.

The lithium catalysts which can be used are typically organolithiumcompounds. The organolithium compounds which are preferred can berepresented by the formula: R--Li, wherein R represents a hydrocarbylradical containing from 1 to about 20 carbon atoms. Generally, suchmonofunctional organolithium compounds will contain from 1 to about 10carbon atoms. Some representative examples of organolithium compoundswhich can be employed include methyllithium, ethyllithium,isopropyllithium, n-butyllithium, sec-butyllithium, n-octyllithium,tert-octyllithium, n-decyllithium, phenyllithium, 1-napthyllithium,4-butylphenyllithium, p-tolyllithium, 1-naphthyllithium,4-butylphenyllithium, p-tolyllithium, 4-phenylbutyllithium,cyclohexyllithium, 4-butylcyclohexyllithium, and4-cyclohexylbutyllithium. Organo monolithium compounds, such asalkyllithium compounds and aryllithium compounds, are usually employed.Some representative examples of preferred organo monolithium compoundsthat can be utilized include ethylaluminum, isopropylaluminum,n-butyllithium, secondary-butyllithium, normal-hexyllithium,tertiary-octyllithium, phenyllithium, 2-napthyllithium,4-butylphenyllithium, 4-phenylbutyllithium, cyclohexyllithium, and thelike. Normal-butyllithium and secondary-butyllithium are highlypreferred lithium initiators.

The amount of lithium catalyst utilized will vary from one organolithiumcompound to another and with the molecular weight that is desired forthe rubber being synthesized. As a general rule in all anionicpolymerizations, the molecular weight (Mooney viscosity) of the polymerproduced is inversely proportional to the amount of catalyst utilized.As a general rule, from about 0.01 phm (parts per hundred parts byweight of monomer) to 1 phm of the lithium catalyst will be employed. Inmost cases, from 0.01 phm to 0.1 phm of the lithium catalyst will beemployed with it being preferred to utilize 0.025 phm to 0.07 phm of thelithium catalyst.

Normally, from about 5 weight percent to about 35 weight percent of themonomer will be charged into the polymerization medium (based upon thetotal weight of the polymerization medium including the organic solventand monomer). In most cases, it will be preferred for the polymerizationmedium to contain from about 10 weight percent to about 30 weightpercent monomer. It is typically more preferred for the polymerizationmedium to contain from about 20 weight percent to about 25 weightpercent monomer.

The polymerization temperature will normally be within the range ofabout 5° C. to about 100° C. For practical reasons and to attain thedesired microstructure the polymerization temperature will preferably bewithin the range of about 40° C. to about 90° C. Polymerizationtemperatures within the range of about 60° C. to about 90° C. are mostpreferred. The microstructure of the rubbery polymer is somewhatdependent upon the polymerization temperature.

The polymerization is allowed to continue until essentially all of themonomer has been exhausted. In other words, the polymerization isallowed to run to completion. Since a lithium catalyst is employed topolymerize the monomer, a living polymer is produced. The living polymersynthesized will have a number average molecular weight which is withinthe range of about 25,000 to about 700,000. The rubber synthesized willmore typically have a number average molecular weight which is withinthe range of about 150,000 to about 400,000.

To increase the level of vinyl content the polymerization is carried outin the presence of at least one polar modifier. Ethers and tertiaryamines which act as Lewis bases are representative examples of polarmodifiers that can be utilized. Some specific examples of typical polarmodifiers include diethyl ether, di-n-propyl ether, diisopropyl ether,di-n-butyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethylether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether,diethylene glycol diethyl ether, triethylene glycol dimethyl ether,trimethylamine, triethylamine, N,N,N',N'-tetramethylethylenediamine,N-methyl morpholine, N-ethyl morpholine, N-phenyl morpholine and thelike.

The modifier can also be a 1,2,3-trialkoxybenzene or a1,2,4-trialkoxybenzene. Some representative examples of1,2,3-trialkoxybenzenes that can be used include1,2,3-trimethoxybenzene, 1,2,3-triethoxybenzene, 1,2,3-tributoxybenzene,1,2,3-trihexoxybenzene, 4,5,6-trimethyl-1,2,3-trimethoxybenzene,4,5,6-tri-n-pentyl-1,2,3-triethoxybenzene,5-methyl-1,2,3-trimethoxybenzene, and 5-propyl-1,2,3-trimethoxybenzene.Some representative examples of 1,2,4-trialkoxybenzenes that can be usedinclude 1,2,4-trimethoxybenzene, 1,2,4-triethoxybenzene,1,2,4-tributoxybenzene, 1,2,4-tripentoxybenzene,3,5,6-trimethyl-1,2,4-trimethoxybenzene,5-propyl-1,2,4-trimethoxybenzene, and3,5-dimethyl-1,2,4-trimethoxybenzene. Dipiperidinoethane,dipyrrolidinoethane, tetramethylethylene diamine, diethylene glycol,dimethyl ether and tetrahydrofuran are representative of highlypreferred modifiers. U.S. Pat. No. 4,022,959 describes the use of ethersand tertiary amines as polar modifiers in greater detail.

The utilization of 1,2,3-trialkoxybenzenes and 1,2,4-trialkoxybenzenesas modifiers is described in greater detail in U.S. Pat. No. 4,696,986.The teachings of U.S. Pat. No. 4,022,959 and U.S. Pat. No. 4,696,986 areincorporated herein by reference in their entirety. The microstructureof the repeat units which are derived from butadiene monomer is afunction of the polymerization temperature and the amount of polarmodifier present. For example, it is known that higher temperaturesresult in lower vinyl contents (lower levels of 1,2-microstructure).Accordingly, the polymerization temperature, quantity of modifier andspecific modifier selected will be determined with the ultimate desiredmicrostructure of the polybutadiene rubber being synthesized being keptin mind.

It has been unexpectedly found that a combination of a metal salt of acyclic alcohol and a polar modifier act synergistically to increase thevinyl content of rubbery polymer synthesized in their presence. Theutilization of this synergistic modifier system can also be employedadvantageously in the synthesis of a wide variety of rubbery polymers,such as high vinyl polybutadiene rubber, styrene-butadiene rubber (SBR),styrene-isoprene-butadiene rubber (SIBR), and isoprene-butadiene rubber.

The metal salt of the cyclic alcohol will typically be a Group Ia metalsalt. Lithium, sodium, potassium, rubidium, and cesium salts arerepresentative examples of such salts with lithium, sodium, andpotassium salts being preferred. Sodium salts are typicaly the mostpreferred. The cyclic alcohol can be mono-cyclic, bi-cyclic ortri-cyclic and can be aliphatic or aromatic. They can be substitutedwith 1 to 5 hydrocarbon moieties and can also optionally containhetero-atoms. For instance, the metal salt of the cyclic alcohol can bea metal salt of a di-alkylated cyclohexanol, such as2-isopropyl-5-methylcyclohexanol or 2-t-butyl-5-methylcyclohexanol.These salts are preferred because they are soluble in hexane. Metalsalts of disubstituted cyclohexanol are highly preferred because theyare soluble in hexane and provide similar modification efficiencies tosodium t-amylate. Sodium mentholate is the most highly preferred metalsalt of a cyclic alcohol that can be empolyed in the practice of thisinvention. Metal salts of thymol can also be utilized. The metal salt ofthe cyclic alcohol can be prepared by reacting the cyclic alcoholdirectly with the metal or another metal source, such as sodium hydride,in an aliphatic or aromatic solvent.

The molar ratio of the metal salt of the cyclic alcohol to the polarmodifier will normally be within the range of about 0.1:1 to about 10:1and the molar ratio of the metal salt of the cyclic alcohol to thelithium initiator will normally be within the range of about 0.01:1 toabout 20:1. It is generally preferred for the molar ratio of the metalsalt of the cyclic alcohol to the polar modifier to be within the rangeof about 0.2:1 to about 5:1 and for the molar ratio of the metal salt ofthe cyclic alcohol to the lithium initiator to be within the range ofabout 0.05:1 to about 10:1. It is generally more preferred for the molarratio of the metal salt of the cyclic alcohol to the polar modifier tobe within the range of about 0.5:1 to about 1:1 and for the molar ratioof the metal salt of the cyclic alcohol to the lithium initiator to bewithin the range of about 0.2:1 to about 3:1.

After the polymerization has been completed, the living rubbery polymercan optionally be coupled with a suitable coupling agent, such as a tintetrahalide or a silicon tetrahalide. The rubbery polymer is thenrecovered from the organic solvent. The polybutadiene rubber can berecovered from the organic solvent and residue by any means, such asdecantation, filtration, centrification and the like. It is oftendesirable to precipitate the rubbery polymer from the organic solvent bythe addition of lower alcohols containing from about 1 to about 4 carbonatoms to the polymer solution. Suitable lower alcohols for precipitationof the rubbery polymer from the polymer cement include methanol,ethanol, isopropyl alcohol, normal-propyl alcohol and t-butyl alcohol.The utilization of lower alcohols to precipitate the rubber from thepolymer cement also "kills" the living polymer by inactivating lithiumend groups. After the rubbery polymer is recovered from the solution,steam stripping can be employed to reduce the level of volatile organiccompounds in the polymer. The inert solvent and residual monomer canthen be recycled for subsequent polymerization.

There are valuable benefits associated with utilizing polybutadienerubber made with the modifiers of this invention in tire treadcompounds. For instance, tire tread compounds can be made by blendingpolybutadiene rubbers having at least three different vinyl contents. Itis normally not necessary to include additional rubbers, such asstyrene-butadiene rubber, in such blends. A highly preferred blend ofthis type contains: (1) super-high vinyl polybutadiene rubber which hasa vinyl content which is within the range of 80 percent to 100 percentand a glass transition temperature which is within the range of about-15° C. to about 0° C., (2) high vinyl polybutadiene rubber which has avinyl content which is within the range of 60 percent to 79 percent anda glass transition temperature which is within the range of about -45°C. to about -40° C., (3) medium vinyl polybutadiene rubber which has avinyl content which is within the range of 35 percent to 59 percent anda glass transition temperature which is within the range of about -75°C. to about -45° C., and (4) low vinyl polybutadiene rubber which has avinyl content which is within the range of 8 percent to 34 percent and aglass transition temperature which is within the range of about -95° C.to about -75° C. It is important for such blends to contain at leastthree of the four members of the group consisting of super-high vinylpolybutadiene rubber, high vinyl polybutadiene rubber, medium vinylpolybutadiene rubber, and low vinyl polybutadiene rubber.

In such blends it is also critical for at least one of the polybutadienerubbers in the blend to have a vinyl content which is within 35percentage points of the vinyl content of at least one otherpolybutadiene rubber in the blend to provide compatibility. It ispreferred for at least one of the polybutadiene rubbers in the blend tohave a vinyl content which is within 30 percentage points of the vinylcontent of at least one other polybutadiene rubber in the blend. It ismore preferred for at least one of the polybutadiene rubbers in theblend to have a vinyl content which is within 25 percentage points ofthe vinyl content of at least one other polybutadiene rubber in theblend. For instance, it would be highly preferred for the blend tocontain a super-high vinyl polybutadiene rubber having a vinyl contentof 90 percent and a high vinyl polybutadiene rubber having a vinylcontent of 65 percent (the vinyl content of the high vinyl polybutadienerubber differs from the vinyl content of the super-high vinylpolybutadiene by only 25 percentage points).

It is also important for the three different polybutadiene rubbersemployed in the blend to have vinyl contents which differ from the othertwo polybutadiene rubbers employed in the blend by at least 5 percentagepoints. In other words, the vinyl contents of the differentpolybutadiene rubbers utilized in the blend must differ by at least 5percentage points. For example, if a super-high vinyl polybutadienerubber having a vinyl content of 80 percent and a high vinylpolybutadiene rubber are employed in the blend, the vinyl content of thehigh vinyl polybutadiene must be less than 75 percent. It is preferredfor the three different polybutadiene rubbers employed in the blend tohave vinyl contents which differ from the other two polybutadienerubbers employed in the blend by at least 10 percentage points. Thus, itwould be highly preferred to utilize a super-high vinyl polybutadienerubber having a vinyl content of 85 percent and a high vinylpolybutadiene rubber having a vinyl content of 70 percent in the blend(there is a 15 percentage point difference between the vinyl contents ofthe two polybutadiene rubbers. Stated in still another way, the vinylcontent of the first polybutadiene rubber can not have a vinyl contentwhich is within 5 percentage points of the vinyl content of the secondpolybutadiene rubber or the third polybutadiene rubber, and the vinylcontent of the second polybutadiene rubber can not have a vinyl contentwhich is within 5 percentage points of the vinyl content of the thirdpolybutadiene rubber.

It is also important for the blend as a whole to have a total vinylcontent of at least 40 percent and preferably 45 percent. The totalvinyl content of the blend as a whole is the sum of the products of thenumber of parts of each of the polybutadiene rubbers included in theblend and the vinyl contents of those polybutadiene rubbers, with thatsum being divided by the total number of parts of polybutadiene rubberincluded in the blend. For example, if the blend included 40 parts of alow vinyl polybutadiene rubber having a vinyl content of 20 percent, 40parts of a medium vinyl polybutadiene rubber having a vinyl content of40 percent, and 20 parts of a super-high vinyl polybutadiene rubberhaving a vinyl content of 80 percent, the blend as a whole would have atotal vinyl content of 40 percent. In another example, if the blendincluded 20 parts of a low vinyl polybutadiene rubber having a vinylcontent of 30 percent, 40 parts of a high vinyl polybutadiene rubberhaving a vinyl content of 60 percent, and 40 parts of a super-high vinylpolybutadiene rubber having a vinyl content of 90 percent, the blend asa whole would have a total vinyl content of 66 percent.

Such polybutadiene rubber blends will contain at least 10 phr (parts per100 parts by weight of rubber) of the first polybutadiene rubber, atleast 10 phr of the second polybutadiene rubber, and at least 10 phr ofthe third polybutadiene rubber. The blend will preferably contain atleast 20 phr of the first polybutadiene rubber, at least 20 phr of thesecond polybutadiene rubber, and at least 20 phr of the thirdpolybutadiene rubber. The blend will more preferably contain at least 25phr of the first polybutadiene rubber, at least 25 phr of the secondpolybutadiene rubber, and at least 25 phr of the third polybutadienerubber.

Such polybutadiene rubber blends can be compounded utilizingconventional ingredients and standard techniques. For instance, thepolybutadiene rubber blends will typically be mixed with carbon blackand/or silica, sulfur, fillers, accelerators, oils, waxes, scorchinhibiting agents, and processing aids. In most cases, the polybutadienerubber blends will be compounded with sulfur and/or a sulfur containingcompound, at least one filler, at least one accelerator, at least oneantidegradant, at least one processing oil, zinc oxide, optionally atackifier resin, optionally a reinforcing resin, optionally one or morefatty acids, optionally a peptizer and optionally one or more scorchinhibiting agents. Such blends will normally contain from about 0.5 to 5phr (parts per hundred parts of rubber by weight) of sulfur and/or asulfur containing compound with 1 phr to 2.5 phr being preferred. It maybe desirable to utilize insoluble sulfur in cases where bloom is aproblem.

Normally from 10 to 150 phr of at least one filler will be utilized inthe blend with 30 to 80 phr being preferred. In most cases at least somecarbon black will be utilized in the filler. The filler can, of course,be comprised totally of carbon black. Silica can be included in thefiller to improve tear resistance and heat build up. Clays and/or talccan be included in the filler to reduce cost. The blend will alsonormally include from 0.1 to 2.5 phr of at least one accelerator with0.2 to 1.5 phr being preferred. Antidegradants, such as antioxidants andantiozonants, will generally be included in the tread compound blend inamounts ranging from 0.25 to 10 phr with amounts in the range of 1 to 5phr being preferred. Processing oils will generally be included in theblend in amounts ranging from 2 to 100 phr with amounts ranging from 5to 50 phr being preferred. The polybutadiene blends of this inventionwill also normally contain from 0.5 to 10 phr of zinc oxide with 1 to 5phr being preferred. These blends can optionally contain from 0 to 10phr of tackifier resins, 0 to 10 phr of reinforcing resins, 1 to 10 phrof fatty acids, 0 to 2.5 phr of peptizers, and 0 to 1 phr of scorchinhibiting agents.

To fully realize the total advantages of such polybutadiene rubberblends, silica will normally be included in the tread rubberformulation. The processing of the polybutadiene rubber blend isnormally conducted in the presence of a sulfur containing organosiliconcompound to realize maximum benefits. Examples of suitable sulfurcontaining organosilicon compounds are of the formula:

    Z--Alk--S.sub.n --Alk--Z                                   (I)

in which Z is selected from the group consisting of ##STR1## where R¹ isan alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; wherein R²is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms;and wherein Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and nis an integer of 2 to 8.

Specific examples of sulfur containing organosilicon compounds which maybe used in accordance with the present invention include:3,3'-bis(trimethoxysilylpropyl) disulfide,3,3'-bis(triethoxysilylpropyl) tetrasulfide,3,3'-bis(triethoxysilylpropyl) octasulfide,3,3'-bis(trimethoxysilylpropyl) tetrasulfide,2,2'-bis(triethoxysilylethyl) tetrasulfide,3,3'-bis(trimethoxysilylpropyl) trisulfide,3,3'-bis(triethoxysilylpropyl) trisulfide,3,3'-bis(tributoxysilylpropyl) disulfide,3,3'-bis(trimethoxysilylpropyl) hexasulfide,3,3'-bis(trimethoxysilylpropyl) octasulfide,3,3'-bis(trioctoxysilylpropyl) tetrasulfide,3,3'-bis(trihexoxysilylpropyl) disulfide,3,3'-bis(tri-2"-ethylhexoxysilylpropyl) trisulfide,3,3'-bis(triisooctoxysilylpropyl) tetrasulfide,3,3'-bis(tri-t-butoxysilylpropyl) disulfide, 2,2'-bis(methoxy diethoxysilyl ethyl) tetrasulfide, 2,2'-bis(tripropoxysilylethyl) pentasulfide,3,3'-bis(tricyclonexoxysilylpropyl) tetrasulfide,3,3'-bis(tricyclopentoxysilylpropyl) trisulfide,2,2'-bis(tri-2"-methylcyclohexoxysilylethyl) tetrasulfide,bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl3'-diethoxybutoxy-silylpropyltetrasulfide, 2,2'-bis(dimethylmethoxysilylethyl) disulfide, 2,2'-bis(dimethyl sec.butoxysilylethyl)trisulfide, 3,3'-bis(methyl butylethoxysilylpropyl) tetrasulfide,3,3'-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2'-bis(phenylmethyl methoxysilylethyl) trisulfide, 3,3'-bis(diphenylisopropoxysilylpropyl) tetrasulfide, 3,3'-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3'-bis(dimethylethylmercaptosilylpropyl) tetrasulfide, 2,2'-bis (methyldimethoxysilylethyl) trisulfide, 2,2'-bis(methylethoxypropoxysilylethyl) tetrasulfide, 3,3'-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3'-bis(ethyl di-sec.butoxysilylpropyl) disulfide, 3,3'-bis(propyl diethoxysilylpropyl)disulfide, 3,3'-bis(butyl dimethoxysilylpropyl) trisulfide,3,3'-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenylethoxybutoxysilyl 3'-trimethoxysilylpropyl tetrasulfide,4,4'-bis(trimethoxysilylbutyl) tetrasulfide,6,6'-bis(triethoxysilylhexyl) tetrasulfide,12,12'-bis(triisopropoxysilyl dodecyl) disulfide,18,18'-bis(trimethoxysilyloctadecyl) tetrasulfide,18,18'-bis(tripropoxysilyloctadecenyl) tetrasulfide,4,4'-bis(trimethoxysilyl-buten-2-yl) tetrasulfide,4,4'-bis(trimethoxysilylcyclohexylene) tetrasulfide,5,5'-bis(dimethoxymethylsilylpentyl) trisulfide,3,3'-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide,3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide.

The preferred sulfur containing organosilicon compounds are the3,3'-bis(trimethoxy or triethoxy silylpropyl) sulfides. The mostpreferred compound is 3,3'-bis(triethoxysilylpropyl) tetrasulfide.Therefore as to formula I, preferably Z is ##STR2## where R² is analkoxy of 2 to 4 carbon atoms, with 2 carbon atoms being particularlypreferred; Alk is a divalent hydrocarbon of 2 to 4 carbon atoms with 3carbon atoms being particularly preferred; and n is an integer of from 3to 5 with 4 being particularly preferred.

The amount of the sulfur containing organosilicon compound of formula Iin a rubber composition will vary depending on the level of silica thatis used. Generally speaking, the amount of the compound of formula Iwill range from about 0.01 to about 1.0 parts by weight per part byweight of the silica. Preferably, the amount will range from about 0.02to about 0.4 parts by weight per part by weight of the silica. Morepreferably the amount of the compound of formula I will range from about0.05 to about 0.25 parts by weight per part by weight of the silica.

In addition to the sulfur containing organosilicon, the rubbercomposition should contain a sufficient amount of silica, and carbonblack, if used, to contribute a reasonably high modulus and highresistance to tear. The silica filler may be added in amounts rangingfrom about 10 phr to about 250 phr. Preferably, the silica is present inan amount ranging from about 15 phr to about 80 phr. If carbon black isalso present, the amount of carbon black, if used, may vary. Generallyspeaking, the amount of carbon black will vary from about 5 phr to about80 phr. Preferably, the amount of carbon black will range from about 10phr to about 40 phr. It is to be appreciated that the silica coupler maybe used in conjunction with a carbon black, namely pre-mixed with acarbon black prior to addition to the rubber composition, and suchcarbon black is to be included in the aforesaid amount of carbon blackfor the rubber composition formulation. In any case, the total quantityof silica and carbon black will be at least about 30 phr. The combinedweight of the silica and carbon black, as hereinbefore referenced, maybe as low as about 30 phr, but is preferably from about 45 to about 130phr.

The commonly employed siliceous pigments used in rubber compoundingapplications can be used as the silica. For instance the silica caninclude pyrogenic and precipitated siliceous pigments (silica), althoughprecipitate silicas are preferred. The siliceous pigments preferablyemployed in this invention are precipitated silicas such as, forexample, those obtained by the acidification of a soluble silicate,e.g., sodium silicate.

Such silicas might be characterized, for example, by having a BETsurface area, as measured using nitrogen gas, preferably in the range ofabout 40 to about 600, and more usually in a range of about 50 to about300 square meters per gram. The BET method of measuring surface area isdescribed in the Journal of the American Chemical Society, Volume 60,page 304 (1930).

The silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, and more usually about 150 to about 300. The silica might beexpected to have an average ultimate particle size, for example, in therange of 0.01 to 0.05 micron as determined by the electron microscope,although the silica particles may be even smaller, or possibly larger,in size.

Various commercially available silicas may be considered for use in thisinvention such as, only for example herein, and without limitation,silicas commercially available from PPG Industries under the Hi-Siltrademark with designations 210, 243, etc; silicas available fromRhone-Poulenc, with, for example, designations of Z1165MP and Z165GR andsilicas available from Degussa AG with, for example, designations VN2and VN3.

Tire tread formulations which include silica and an organosiliconcompound will typically be mixed utilizing a thermomechanical mixingtechnique. The mixing of the tire tread rubber formulation can beaccomplished by methods known to those having skill in the rubber mixingart. For example the ingredients are typically mixed in at least twostages, namely at least one non-productive stage followed by aproductive mix stage. The final curatives including sulfur vulcanizingagents are typically mixed in the final stage which is conventionallycalled the "productive" mix stage in which the mixing typically occursat a temperature, or ultimate temperature, lower than the mixtemperature(s) than the preceding non-productive mix stage(s). Therubber, silica and sulfur containing organosilicon, and carbon black ifused, are mixed in one or more non-productive mix stages. The terms"non-productive" and "productive" mix stages are well known to thosehaving skill in the rubber mixing art. The sulfur vulcanizable rubbercomposition containing the sulfur containing organosilicon compound,vulcanizable rubber and generally at least part of the silica should besubjected to a thermomechanical mixing step. The thermomechanical mixingstep generally comprises a mechanical working in a mixer or extruder fora period of time suitable in order to produce a rubber temperaturebetween 140° C. and 190° C. The appropriate duration of thethermomechanical working varies as a function of the operatingconditions and the volume and nature of the components. For example, thethermomechanical working may be for a duration of time which is withinthe range of about 2 minutes to about 20 minutes. It will normally bepreferred for the rubber to reach a temperature which is within therange of about 145° C. to about 180° C. and to be maintained at saidtemperature for a period of time which is within the range of about 4minutes to about 12 minutes. It will normally be more preferred for therubber to reach a temperature which is within the range of about 155° C.to about 170° C. and to be maintained at said temperature for a periodof time which is within the range of about 5 minutes to about 10minutes.

Tire tread compounds made using such polybutadiene rubber blends can beused in tire treads in conjunction with ordinary tire manufacturingtechniques. Tires are built utilizing standard procedures with thepolybutadiene rubber blend simply being substituted for the rubbercompounds typically used as the tread rubber. After the tire has beenbuilt with the polybutadiene rubber containing blend, it can bevulcanized using a normal tire cure cycle. Tires made in accordance withthis invention can be cured over a wide temperature range. However, itis generally preferred for the tires to be cured at a temperatureranging from about 132° C. (270° F.) to about 166° C. (330° F.). It ismore typical for the tires of this invention to be cured at atemperature ranging from about 143° C. (290° F.) to about 154° C. (310°F.). It is generally preferred for the cure cycle used to vulcanize thetires to have a duration of about 10 to about 20 minutes with a curecycle of about 12 to about 18 minutes being most preferred.

By utilizing such polybutadiene rubber blends in tire tread compounds,traction characteristics can be improved without compromising tread wearor rolling resistance. Since such polybutadiene rubber blends do notcontain styrene the cost of raw materials can also be reduced. This isbecause styrene and other vinyl aromatic monomers are expensive relativeto the cost of 1,3-butadiene.

This invention is illustrated by the following examples which are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, all parts and percentages aregiven by weight.

EXAMPLE 1

In this experiment, 2300 g of a silica/alumina/molecular sieve driedpremix containing 11.0 weight percent 1,3-butadiene was charged into aone-gallon (3.8 liters) reactor. After the impurity of 1.5 ppm wasdetermined, 7.42 ml of 1M solution of N,N,N',N'-tetramethylethylenediamine (TMEDA) in hexanes, 0.21 ml of 1.12M solution of sodiummentholate (SMT) in hexanes and 1.1 ml of a 1.03M solution ofn-butyllithium (n-BuLi) in hexanes (0.9 ml for initiation and 0.2 ml forscavenging the premix) were added to the reactor. The molar ratio of SMTto TMEDA and to n-BuLi was 0.25:8:1.

The polymerization was carried out at 65° C. for 10 minutes. The GCanalysis of the residual monomer contained in the polymerization mixtureindicated that the polymerization was complete at this time. Then one mlof 1M ethanol solution in hexanes was added to shortstop thepolymerization and polymer was removed from the reactor and stabilizedwith 1 phm of antioxidant. After evaporating hexanes, the resultingpolymer was dried in a vacuum oven at 50° C.

The polybutadiene produced was determined to have a glass transitiontemperature (Tg) at -25° C. It was then determined to have amicrostructure which contained 85 percent 1,2-polybutadiene units and 15percent 1,4-polybutadiene units. The Mooney ML-4 viscosity at 100° C.was 83 for this polybutadiene.

EXAMPLES 2-8

The procedure described in Example 1 was utilized in these examplesexcept that the SMT/TMEDA/n-BuLi ratio was varied. The Tgs and ML-4s ofthe resulting polybutadienes are listed in Table I.

                  TABLE I                                                         ______________________________________                                        Example   SMT/TMEDS/n-BuLi Ratio                                                                         Tg (° C.)                                                                        ML-4                                     ______________________________________                                        1         0.25:8:1         -25.4     83                                         2 0.25:5:1 -26.9 81                                                           3 0.25:3:1 -28.9 87                                                           4 0.25:1:1 -35.6 88                                                           5 0.25:0.5:1 -49.2 88                                                         6 0.15:3:1 -26.9                                                              7 0.5:3:1 -26.5 81                                                            8 1:3:1 -26.1                                                               ______________________________________                                    

EXAMPLE 9

The procedure described in Example 1 was utilized in this example exceptthat isoprene was used as the monomer and the SMT/TMEDA/BuLi ratio waschanged to 0.5:3:1. It took about 20 minutes to complete thepolymerization. The polymer was determined to have a Tg at -2° C. and aML-4 of 60 at 100° C.

EXAMPLES 10-13

The procedure described in Example 1 was utilized in these examplesexcept for the fact that a mixture of styrene and 1,3-butadiene inhexane was employed as the monomer solution and that theSMT/TMEDA/n-BuLi ratio was varied as shown in Table II. Thepolymerization temperature was also changed to 90° C. The glasstransition temperatures of the resulting styrene-butadiene rubber (SBR)and the time required to complete the polymerization are also shown inTable II. The styrene sequence distributions in all of the SBR producedwas random.

                  TABLE II                                                        ______________________________________                                        Example                                                                              S:Bd    SMT/TMEDA/n-BuLi                                                                             Tg (° C.)                                                                      Time                                    ______________________________________                                        10     40:60   0.25:2:1       -19     5 min.                                    11 45:55 0.25:2:1 -8 4 min.                                                   12 50:50 0.25:2:1 +5 2 min.                                                   13 60:40 0.25:2:1 -14 3 min.                                                ______________________________________                                    

EXAMPLES 14-18

The procedure described in Example 1 was utilized in these examplesexcept that a mixture of styrene and 1,3-butadiene in hexanes was usedas the monomer solution and the SMT alone was used as the modifier. Thepolymerization temperature was also changed to 90° C. The glasstransition temperatures of the resulting SBR and the time required tocomplete the polymerizations are listed in Table III. The sequencedistributions of all of the SBR samples made was again random.

                  TABLE III                                                       ______________________________________                                        Example   S:Bd     SMT/n-BuLi Tg (° C.)                                                                     Time                                     ______________________________________                                        14        10:90    0.2:1      -72    15 min.                                    15 15:85 0.2:1 -63 25 min.                                                    16 20:80 0.2:1 -65 15 min.                                                    17 25:75 0.2:1 -54 20 min.                                                    18 20:80 0.15:1 -80 40 min.                                                 ______________________________________                                    

Variations in the present invention are possible in light of thedescription of it provided herein. It is, therefore, to be understoodthat changes can be made in the particular embodiments described whichwill be within the full intended scope of the invention as defined bythe following appended claims.

What is claimed is:
 1. An initiator system which is comprised of (a) alithium initiator, (b) a group Ia metal salt of a di-alkylatedcyclohexanol, and (c) a polar modifier; wherein the molar ratio of themetal salt of the di-alkylated cyclohexanol to the polar modifier iswithin the range of about 0.1:1 to about 10:1; and wherein the molarratio of the metal salt of the di-alkylated cyclohexanol to the lithiuminitiator is within the range of about 0.01:1 to about 20:1.
 2. Aninitiator system as specified in claim 1 wherein the metal salt of thecyclic alcohol is a salt of a metal selected from the group consistingof lithium, sodium, potassium, rubidium, and cesium.
 3. An initiatorsystem as specified in claim 1 wherein the molar ratio of the group Iametal salt of the di-alkylated cyclohexanol to the polar modifier iswithin the range of about 0.2:1 to about 5:1; and wherein the molarratio of the metal salt of the cyclic alcohol to the lithium initiatoris within the range of about 0.05:1 to about 10:1.
 4. A process asspecified in claim 1 wherein the group Ia metal salt of the di-alkylatedcyclohexanol is a group Ia metal salt of a metal selected from the groupconsisting of lithium, sodium, potassium, rubidium, and cesium.
 5. Aprocess for preparing a rubbery polymer having a high vinyl contentwhich comprises polymerizing at least one diene monomer at a temperaturewhich is within the range of about 5° C. to about 100° C. in thepresence of the initiator system specified in claim
 1. 6. A process forpreparing high vinyl polybutadiene rubber which comprises polymerizing1,3-butadiene monomer at a temperature which is within the range ofabout 5° C. to about 100° C. in the presence of the initiator systemspecified in claim
 1. 7. A process as specified in claim 5 wherein saidpolar modifier is selected from the group consisting of diethyl ether,di-n-propyl ether, diisopropyl ether, di-n-butyl ether, tetrahydrofuran,dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether,diethylene glycol dimethyl ether, diethylene glycol diethyl ether,triethylene glycol dimethyl ether, trimethylamine, triethylamine,N,N,N',N'-tetramethylethylenediamine, N-methyl morpholine, N-ethylmorpholine, N-phenyl morpholine, and alkyltetrahydrofurfuryl ethers. 8.A process as specified in claim 5 wherein the lithium initiator is analkyl lithium compound.
 9. A process as specified in claim 8 wherein themolar ratio of the group Ia metal salt of the di-alkylated cyclohexanolto the polar modifier is within the range of about 0.2:1 to about 5:1;and wherein the molar ratio of the group Ia metal salt of thedi-alkylated cyclohexanol to the lithium initiator is within the rangeof about 0.05:1 to about 10:1.
 10. A process as specified in claim 5wherein the polymerization is conducted at a temperature which is withinthe range of about 40° C. to about 90° C.
 11. A process as specified inclaim 5 wherein said polymerization is conducted in an inert organicsolvent.
 12. A process as specified in claim 11 wherein the group Iametal salt of the di-alkylated cyclohexanol is sodium mentholate.
 13. Aprocess as specified in claim 12 wherein the molar ratio of the group Iametal salt of the sodium mentholate to the polar modifier is within therange of about 0.5:1 to about 1:1; and wherein the molar ratio of thegroup Ia metal salt of the sodium metholate to the lithium initiator iswithin the range of about 0.2:1 to about 3:1.
 14. A process as specifiedin claim 5 wherein the lithium initiator is n-butyl lithium.
 15. Aprocess as specified in claim 5 wherein said polar modifier isN,N,N',N'-tetramethyl ethylenediamine.
 16. A process as specified inclaim 13 wherein the polymerization is conducted at a temperature whichis within the range of about 60° C. to about 90° C.
 17. A process asspecified in claim 5 wherein the rubbery polymer is coupled after thepolymerization has been completed.
 18. A process as specified in claim 5wherein the coupling is carried out utilzing a tin tetrahalide.
 19. Aninitiator system which is comprised of (a) a lithium initiator, (b) agroup Ia metal salt of a disubstituted cyclohexanol, and (c) a polarmodifier; wherein the molar ratio of the metal salt of the disubstitutedcyclohexanol to the polar modifier is within the range of about 0.1:1 toabout 10:1; and wherein the molar ratio of the metal salt of thedisubstituted cyclohexanol to the lithium initiator is within the rangeof about 0.01:1 to about 20:1.
 20. An initiator system which iscomprised of (a) a lithium initiator, (b) sodium mentholate, and (c) apolar modifier; wherein the molar ratio of the sodium mentholate to thepolar modifier is within the range of about 0.1:1 to about 10:1; andwherein the molar ratio of the sodium mentholate to the lithiuminitiator is within the range of about 0.01:1 to about 20:1.
 21. Aninitiator system as specified in claim 20 wherein the molar ratio of thesodium mentholate to the polar modifier is within the range of about0.5:1 to about 1:1; and wherein the molar ratio of the sodium mentholateto the lithium initiator is within the range of about 0.2:1 to about3:1.
 22. A process for preparing high vinyl polybutadiene rubber whichcomprises polymerizing 1,3-butadiene monomer at a temperature which iswithin the range of about 5° C. to about 100° C. in the presence of theinitiator system specified in claim
 20. 23. A process as specified inclaim 22 wherein said polymerization is conducted in an inert solvent ata temperature that is within the range of about 40° C. to about 90° C.